1) Field of the Invention
This invention relates to structures and methods of filling contact holes and forming metal patterns in semiconductor devices.
2) Description of the Prior Art
In the fabrication of semiconductor devices, electrical interconnections (i.e., contacts or plugs) are typically made by forming contact holes in a dielectric isolation layer to expose regions of the semiconductor device to which electrical contact must be made, and depositing a metal plug in each contact hole. Next, a metal layer is formed over the plug and dielectric layer. The metal layer is then formed into a metal pattern using conventional photolithographic/etching techniques. While in the past this metal deposition and photo/etching technique has proved effective, the smaller metal pattern line widths of present and future technologies create problems which need to be addressed.
In a conventional process for forming interconnections and metal patterns, shown in FIG. 1, an oxide layer 12 is formed on a substrate 10. A contact hole 14 having sidewalls 16 and a bottom surface 18 is formed in the oxide layer 12. A conformal adhesion layer 20 is formed over the exposed surfaces 12, 16, and 18. The adhesion layer 20, which can be formed of Ti and TiN, is used to promote the selective deposition of the plug metal 22 that fills the contact hole 14. Next, the contact hole 14 is substantially filled with a spin on glass layer which masks the underlying adhesion layer 20. The unmasked adhesion layer is etched away and then the spin on glass layer is removed. A contact metal 22 (interconnect or plug), such as tungsten, is deposited and etched back to fill the contact hole 14. Then a metal layer 24, such as aluminum, is formed on the exposed surfaces. Next, conventional photolithographic and etch processes are used to form the metal layer into a metal line pattern.
This conventional process has several disadvantages. Two metal depositions are use to form the plug 22 and the metal line pattern which increases costs and process complexity. Moreover, as the metal line widths decrease, the conventional photolithographic processes have less precision and increase in cost. With the conventional process, it is difficult to define metal lines by etching without forming "stringers". To remove metal stringers, the metal line pattern must be intensively over etched thereby increasing manufacturing costs and reducing line resolution. Moreover, the metal line resolution is limited by the metal etch "loading effect", especially for 0.5 micron and smaller line patterns. Therefore, metal line resolution could be improved if the metal lines were defined by a more accurate, non-etch process.
Also, special photoresist processes for metals, such as Anti-Reflection-Coating (ACR) and thick photo resist, are required for increased resolution and to compensate for the erosion of the photoresist. Thick photoresist is required to compensate for photoresist that is eroded during the metal overetch so that the metal lines are not exposed.
It is desirous to develop a process and structure whereby the metal line patterns are defined by an easier, cheaper, and more precise process than the conventional photo process. Also desirous is a process whereby the contact plug and metal pattern layer could be accurately formed in one metal deposition step with improved metal line resolution.
The following U.S. patent provide additional background for forming contact plugs and metal line patterns.
U.S. Pat. No. 4,898,841 to Ho teaches a method of filling contact holes whereby a tungsten silicide layer is formed on the sidewalls of a contact hole.
U.S. Pat. No. 5,219,789 to Adan discloses a method of forming a contact whereby a spin-on-glass layer is used to mask a TiW adhesion layer which coats the surfaces of a contact hole. This is used to form TiW adhesion layer along side wall and bottom of a contact hole for a subsequent selective metal chemical vapor deposition.
U.S. Pat. No. 5,187,120 to Wang discloses a contact formation method whereby a first TiN layer is formed on the bottom of a contact hole in a dielectric layer to promote the nucleation of tungsten. A second layer that resists nucleation of tungsten is formed on the surface of the dielectric layer.
U.S. Pat. No. 4,884,123 to Dixit et al., teaches a contact plug employing a Ti/TiN layer lining the contact hole and on the surface of the top insulation layer. However, two metal depositions are used to form the contact plug and the metal pattern layer. Also, the metal lines are defined by a conventional photo process.
While these methods improve the reliability and manufacturability of electrical contacts and metal layers, further improvement is desirable.